1. Field of the Invention
The invention relates to a method of film deposition and, more particularly, to a titanium nitride film deposition process using a metallo-organic precursor.
2. Description of the Background Art
Titanium nitride (TiN) film is widely used as a barrier or contact layer in integrated circuit fabrication, particularly for device applications. A TiN film may be formed by metallo organic chemical vapor deposition (MOCVD) using precursors such as tetrakis (dialkylamino)-titanium, or Ti(NR2)4, where R is an alkyl group. For example, U.S. Pat. No. 5,246,881, issued on Sep. 21, 1993, discloses thermal decomposition of tetrakis (dimethylamino)-titanium, or TDMAT, in combination with an activated species, for TiN deposition at temperatures of 200-600xc2x0 C. and pressures of about 0.1 to 100 torr. Another U.S. Pat. No. 5,576,071 (""071 patent), issued on Nov. 19, 1996, discloses a similar TiN deposition process in the presence of a reactive carrier gas such as nitrogen at a pressure of 0.1-10 torr and a temperature in the range of 200-700xc2x0 C.
While the choice of deposition parameters is primarily dictated by the desired electrical and physical characteristic of the deposited film, it is also constrained by the need for compatibility with other materials already present on the wafer substrate. For example, for sub-0.25 xcexcm device applications, the capacitance of metal interconnects can contribute significantly to signal delays. To satisfy both circuit speed and cross-talk requirements between metal interconnects, it is preferable that insulators be made of materials having a low dielectric constant (i.e., low xcexa dielectric materials having xcexa less than 3.8). However, current low xcexa dielectric materials, which include a wide variety of fluorinated organic or inorganic compounds, are stable only up to about 400xc2x0 C. Thus, backend processes including TiN deposition should preferably be performed at relatively low temperatures to ensure compatibility with these low xcexa dielectrics and avoid adverse effects in device characteristics. However, deposition of TiN using a metallo-organic precursor at temperatures compatible with low xcexa dielectric materials has a slow deposition rate.
Therefore, a need exists in the art for a relatively low temperature TiN deposition process which is compatible with low xcexa dielectrics materials, without sacrificing the deposition rate necessary for a viable device manufacturing process.
The disadvantages associated with the prior art are overcome by a method of depositing a titanium nitride (TiN) film by supplying to a chamber containing a substrate a metallo-organic compound, a dilutant gas, and a purge gas having a flow rate of at least 500 sccm to produce a pressure within the chamber of at least about 5 torr, and heating the substrate to cause thermal decomposition of said metallo-organic compound to form a TiN film upon the substrate.
More specifically, precursor molecules such as tetrakis dialkylamino-titanium (TDMAT) are used in this thermal decomposition process such that TDMAT is decomposed at a sufficiently low temperature to ensure process compatibility with dielectric materials having relatively low dielectric constants (e.g., xcexa less than 3.8) and without substantial reduction in deposition rate obtained by high temperature TiN deposition processes.
In the present invention, the wafer is maintained at a relatively constant processing temperature which is low enough to maintain stability for most of the low xcexa materials used for sub-0.25 xcexcm device fabrication. TDMAT, along with carrier and dilutant gases such as helium and nitrogen, are introduced into a process chamber where thermal decomposition of TDMAT occurs in close proximity to the heated wafer surface. The wafer is preferably kept at a temperature below 350xc2x0 C. through thermal contact with a heated support pedestal. During film deposition, a total pressure in the deposition chamber is maintained at approximately 5 torr, with a nitrogen flow rate of about 1000 sccm, helium flow rate of about 600 sccm, and a wafer backside gas pressure of about 3.5 torr.
In accordance with one aspect of the present invention, a dual-purge gas flow of nitrogen at a rate greater than 1000 sccm is used to minimize undesirable deposit on the edge of the heated pedestal, as well as on the surfaces of an edge ring assembly that circumscribes the pedestal. Furthermore, this purge flow contributes to improving the deposition rate and step coverage of the deposited film.
The present invention allows titanium nitride (TiN) film to be deposited at a relatively high rate of greater than 6 xc3x85/sec., along with improved uniformity, step coverage, and thermal conduction between the wafer and the heated pedestal.
The as-deposited TiN film is subsequently subject to a plasma treatment or annealing step in the presence of hydrogen and nitrogen. The treated TiN film, having a much reduced resistivity compared to the pre-treated film, is suitable for use as a diffusion or contact barrier.
The reduced temperature TiN deposition process of the present invention is fully compatible with the low temperature requirement imposed by the presence of low xcexa dielectric materials. Moreover, the dual-purge capability of the present invention provides a deposit-free, and thus maintenance-free, pedestal heater, and mitigates the problems of micro-arcing and particulate contamination of process wafers.